"This is not the first time EPA has sought to convert the Clean Air Act into a mandate for cost-effective regulation. Whitman v. American Trucking Assns., Inc., 531 U. S. 457 (2001), confronted EPA's contention that it could consider costs in setting [National Ambient Air Quality Standards]," Scalia wrote in his dissent, which was joined by Justice Clarence Thomas.

The problem: the EPA's position in the 2001 case was exactly the opposite. The agency was defending its refusal to consider cost as a counter-weight to health benefits when setting certain air quality standards. It was the trucking industry that wanted the EPA to factor in cost. The 9-0 ruling sided with the EPA.